Satire under fire: can satire be defamatory?

According to Gawker there's been a bit of a barney in the US this week, between 'media futurist' Jeff Jarvis, and a satirical knock off @ProfJeffJarvis. It went like this.

Esquire magazine published an article by "Prof. Jeff Jarvis", although the biography stated that it was not the real Jarvis. The photo showed a fat man in beer helmet. The article itself was pretty obviously a joke, advocating the creation of an Innovation Party, in which (among other things):

"Netizens will be co-opted to both fly drones over Pakistan, East Africa, and other trouble spots, and also to make the difficult call: Does this house really look like it is harboring terrorists? And should we deploy a Hellfire missile at the house or not? Cast your votes!"